feat(host-runtime,llm-replay): keyless llm seam + replay pacing/consumption handle

BootHostOptions.llm: 'deepseek' | false — false mounts no adapter, boots
keyless, and leaves the llm capability seam open for the embedder to fill
on RunningHost.ctx (now the third sanctioned ctx use, JSDoc + README
amended); an unfilled seam fails loud with NO_ADAPTER at the first stream.

dsh-llm-replay grows two additive surfaces for the web browser e2e lane:
paceMs (validated per-chunk delay so a real transport shows incremental
delivery; abort during a pace wait cancels promptly) and a ReplayHandle
return — dispose() plus assertConsumed(), the teardown check that every
recorded script bound and drained, converting silent fixture underruns
into diagnostics. Existing callers updated; config catalog regenerated.

packages/host/runtime/tests/host-runtime.spec.ts

@@ -205,6 +205,42 @@ describe('bootHost / startHost', () => {
     expect((await ctx.sessionTitle.refresh(agent.session))?.source).toEqual({ kind: 'fallback' })
     expect(agent.session.events.some(event => event.type === 'session/title-llm-request')).toBe(false)
   })
+
+  it('llm: false boots keyless with no adapter and fails loud at the first stream', async () => {
+    vi.stubEnv('DEEPSEEK_API_KEY', '')
+    const handle: HostHandle = await bootHost({
+      persistenceRoot: mkdtempSync(join(tmpdir(), 'dsh-boot-keyless-')),
+      workspaceContext: false,
+      llm: false,
+    })
+    // The seam is open: nothing routes 'deepseek', so misuse surfaces at the
+    // earliest resolvable point instead of silently doing provider I/O.
+    await expect(async () => {
+      for await (const chunk of handle.ctx.llm.stream({
+        provider: 'deepseek',
+        model: 'deepseek-v4-flash',
+        messages: [],
+      })) void chunk
+    }).rejects.toThrow(/NO_ADAPTER|no adapter/i)
+    // The embedder can fill the open seam on the returned ctx (the sanctioned
+    // RunningHost.ctx use) and streams route through the filled adapter.
+    class ProbeAdapter extends LlmAdapter {
+      async * stream(): AsyncIterable<StreamChunk> {
+        yield * textResponse('keyless-ok')
+      }
+    }
+    handle.ctx.llm.registerAdapter(['deepseek'], new ProbeAdapter())
+    const collected: string[] = []
+    for await (const chunk of handle.ctx.llm.stream({
+      provider: 'deepseek',
+      model: 'deepseek-v4-flash',
+      messages: [],
+    })) {
+      if (chunk.type === 'text-delta') collected.push(chunk.text)
+    }
+    expect(collected.join('')).toBe('keyless-ok')
+    await handle.dispose()
+  })
 })
 
 describe('host.describe', () => {